1. Field of the Invention
The embodiments of the invention relate to a device for producing a unidirectional (UD) layer from a predetermined number of filament strands with a dispenser arrangement for delivering the filament strands, a storage arrangement for temporary storage of the filament strands, a spreading arrangement and an outlet.
Furthermore, the embodiments of the invention relate to a method for producing a UD layer from a predetermined number of filament strands, which are drawn off from a dispenser arrangement, in which the filament strands are spread apart to form bands. The filament strands are guided through a storage arrangement between the pull-off and the spreading and to an outlet after the spreading.
2. Discussion of Background Information
A device of this type and a method of this type are known, for example from DE 698 19 699 T2.
DE 10 2005 008 705 B3 shows a device for feeding bands to a knitting machine, in which bands are drawn off from bobbins at a uniform speed, but are further processed with predetermined stoppage times. During the stoppage times the bands are temporarily stored in a controlled store.
From DE 10 2005 052 660 B3 a device and a method are known for spreading a carbon fiber strand. In order to be better able to spread out the fiber strand, it is heated in that an electric current is conducted through.
DE 197 07 125 A1 describes a method for producing unidirectional scrims, in which the spread-out fibers are connected to one another by transverse connecting threads in order to form a web.
In the production of fiber-reinforced plastics, the aim is to give these plastics a certain tensile strength. This tensile strength is caused by the reinforcing fibers. The tensile strength is greatest in the direction in which the reinforcing fibers run. Accordingly, it is advantageous to align the reinforcing fibers of a layer all in one direction. A layer of this type is then referred to as a “unidirectional layer” or a “UD layer.” In a UD layer, a plurality of fibers or filaments lies virtually parallel next to one another in one direction. UD layers of this type are used to produce a monoaxial, biaxial or multiaxial scrim. In a multiaxial scrim, several UD layers of this type with different directions are laid on top of one another and connected to one another.
The fibers or filaments that are required in order to reinforce the fiber-reinforced plastic are present in the form of filament strands or filament bundles. In the case of carbon filaments, a filament strand of this type often contains several thousand individual filaments. It is customary for strands to contain 12,000, 24,000, 50,000 or even 480,000 fibers or filaments. It must be possible to handle the filaments of a filament strand together.
The filament strands are wound on bobbins, for example. Before processing, the filament strands then must be drawn off from the bobbins. Although it can be assumed that the filament strands are all wound onto the bobbins with approximately the same tension, local differences arise that lead to corresponding local changes in the filament strands. When the individual filament strands are then spread out to form bands and arranged next to one another, the problem often arises that the UD layer thus produced does not lie flat but warping occurs, which makes a later processability difficult. For example, it is then more difficult to drape a cut-to-length UD layer in a mold before a plastic matrix is poured in.
In the method known from DE 698 19 699 T2 or DE 197 07 125 A1, the bands are provided with a transverse cohesion after the filament strands have been spread, so that a UD layer cohesive in the transverse direction is produced. This layer is then wound onto a beam. To produce a multiaxial scrim, this UD layer can then be drawn off from the beam and processed. The aim is to minimize the effects of the differences of the bands by means of the transverse cohesion.
A scrim that has been provided with a cohesion in the transverse direction, however, has certain disadvantages in further processing. In extreme cases, a UD layer with transverse cohesion can be deformed in only one direction, namely such that the filaments are bent. Due to the transverse cohesion a displacement of the filaments in the longitudinal direction relative to one another is virtually no longer possible or no longer possible to a satisfactory extent.